Effect of Ultrasound Application on Rheological, Physicochemical and Microbiological Properties of Yogurt
Project no. 20728 · Status: Kapanmış · 2019
Summary
<p>In the first part of our study, the effect of ultrasound treatment applied to milk at 90, 180, 300 and 400W powers for 15 min on milk fat globule size and homogenization efficiency compared to classical homogenization at 150 bar pressure was investigated. According to the results obtained, it was determined that ultrasound application is more effective in reducing the diameters of milk fat globules compared to the classical homogenization. As the applied ultrasound power increased, the efficiency of reducing the diameters of milk fat globules increased and the maximum reduction in fat globule size and the best homogenization efficiency was detected in 400W 15 min ultrasound application.</p><p>In the second part of our study, yoghurt was produced using one or two-stage ultrasound application and two different yoghurt cultures (normal and exopolysaccharide (EPS) - producing). In the one-stage ultrasound application, 400W ultrasound determined in the previous stage of the study was applied to milk for 15 min. In the two-stage ultrasound application, in addition to 400W ultrasound, 120W ultrasound was applied to the culture inoculated milk for 5 min.</p><p>Two-stage ultrasound application shortened the fermentation time of yogurts and the lowest fermentation time was determined in the N2 group in yoghurts produced with normal yoghurt culture, and in the E2 group in those produced with EPS-producing yoghurt culture (p<0.05). Ultrasound application positively affected the pH, lactic acid % of yoghurts and the viability of yoghurt bacteria (p<0.05). Differences were found in these properties depending on the culture used (p<0.05).</p><p>While the viscosity of yoghurts produced with EPS-producing yoghurt culture was not affected by ultrasound application (p>0.05), ultrasound application increased viscosity (p<0.05) during storage in yoghurts produced with normal yoghurt culture. In addition, the use of EPS-producing yogurt culture caused a decrease in viscosity (p <0.05). In all yoghurt groups applied ultrasound, an increase in water holding capacity was obtained (p<0.05) compared to control samples at the end of storage and the highest water holding capacity of yoghurts produced with both cultures was determined in E2 and N2 groups, where ultrasound was applied in two stages, at the end of storage. Serum separation of ultrasound applied yoghurts was found less than the control samples (p<0.05). Higher water holding capacity and serum seperation were observed in yoghurts produced with EPS-producing culture.</p><p>It has been determined that the ultrasound application positively affected the free fatty acids of yoghurt samples towards to the end of storage (mostly on the 14th and 28th storage days). Although some fluctuations are seen, ultrasound applications (in one or two stages) on the mentioned storage days decreased the saturated fatty acids values and increased the monounsaturated fatty acids and polyunsaturated fatty acids values of yoghurts. It was determined that the ultrasound application did not cause a significant change in the taste, texture, consistency, appearance, odor and total acceptability of yoghurt samples compared to the control groups (p> 0.05).</p>